Before downgrading, make sure you meet the following requirements
Your PSP is not a TA-082 (If you do have this PSP version, it may result in a brick).
Your PSP hs been upgraded at least once
PLEASE NOTE I WILL NOT BE HELD RESPONSIBLE IF THIS CAUSES YOUR PSP TO BRICK
How to tell if you are using a TA-082 motherboard on your PSP?
Let's get started:
Download the 1.50 helper ( http://dl.qj.net/1.50-helper-%282.5-2.6 … /catid/151 )
1) Copy the folders downhelper and downhelper% from the folder 1.50 HELPER folder to /PSP/GAME/ in your memstick.
2) Obtain the 1.50 update and put it in /PSP/GAME/UPDATE in your memstick. Get it here ( http://www.psp-hacks.com/file/8 )
3) Init the downhelper program.
4) It will dump your flash and some files from the updater eboot to the memstick.
5) After that, the program will exit. You can now delete the updater from /PSP/GAME/UPDATE
6) You'll notice that you have a new folder in the root of your memstick called "DOWNDATER".
7) That's the folder you'll have to send to a 2.50/2.60 to let him test the downgrade.
2.5 / 2.6 User
If you have a 2.5 psp download this file ( http://www.psp-hacks.com/file/598 )
If you have a 2.6 psp download this file ( http://www.psp-hacks.com/file/597 )
1) Copy the folder the DOWNGRADER/2.50/DOWNDATERTEST if you have 2.50 or DOWNGRADER/2.60/DOWNDATERTEST if you have 2.60 to /PSP/GAME/ in your memstick
2) Wait for someone with 1.50 to pass you a folder called DOWNDATER and copy it to the root of your memstick.
3) Init GTA and the eLoader (Search if you do not know how to install the eLoader)
4) In the eLoader menu, choose the downdater test. WARNING: the program won't output any display and any warnings, it will init the downgrader process inmediatelly.
5) You'll see that your memstick flashing. That means that your psp is being flashed from the memstick.
6) You won't see any type of output in the screen (this is for safety). When the memstick finishes of flashing, WAIT at least a minute, and then reinit your psp by holding the power button.
7) That's all. If all went right, you'll have 1.50. If it went less good, you'll still have 2.50/2.60. If all went wrong, you'll have a bricked psp(except in the case you have the modchip) Remember that you have accepted that risk.
8) If your PSP is showing up as v2.01, this is fine. Just use Wab Version Changer and change it to v1.50